In general, the systems which showed the poorest performance did 

 not necessarily give low final electrical resistances. Conversely, the coatings 

 with the lowest final resistances were not necessarily those that performed 

 the least well. 



Prior experiments with coatings that showed appreciable deterioration 

 under laboratory immersion had indicated some correlation between electrical 

 properties and performance."-^^ However, no such apparent correlation exists 

 for the present series of coatings, all of which perform well in laboratory expo- 

 sure. 



Changes in electrical properties, as determined in these experiments, 

 cannot in themselves be used to reliably predict performance. Since the changes 

 are related to changes within the coating it is possible that these changes, together 

 with other factors and other changes in properties, could be used to predict 

 performance. Such an investigation is presently being conducted at NCEL. 



CONCLUSIONS 



1 . As demonstrated in earlier experiments with coating systems of widely 

 varying performance, coatings with strong decreases in resistance or strong 

 increases in capacitance generally do not perform as well. Coatings which 

 show little change in electrical properties generally perform well. 



2. For coatings of comparatively high performance, the changes in electrical 

 properties (including AC resistance, capacitance, and dissipation factor, as 

 well as DC resistance) show correlation with the relative performance in field 

 exposure. However, this correlation is not sufficiently high to allow reliable 

 prediction of comparative performance of good coatings. 



3. Although the changes in electricalproperties of coatings immersed in 

 seawater do not in themselves reliably predict performance, there is the possi- 

 bility that such changes may be useful criteria when considered together with 

 results from other accelerated tests. 



4. The qualification requirement proposed for the Royal Canadian Navy 

 (that coated panels, similar to those used in the present experiments, maintain 

 a DC resistance of 10^ ohms after 1 year of immersion) may be useful in 

 accepting only coatings of high performance, but it would also reject many 

 coatings of high performance. 



5. Neither the dissipation factors of coatings immersed for a short time in 

 seawater, nor the curves of the dissipation factors versus frequency, appear useful 

 in predicting the peformance of coatings. 



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